Metal coated refractory and process of manufacturing same



United States Patent ()fiice 3,129,063 Patented Apr. 14, 1964 This invention relates to a new and improved metal coated refractory and to the method of making the same.

Electrically conductive refractories, such as silver coated refractories, are known but usually they have been made by firing on to the refractories coatings comprising (a) finely divided silver particles and (b) a vitrifiable flux dispersed in a liquid vehicle.

It is an object of this invention to provide a new method of applying a firmly adhering coating of a conducting metal to an underlying refractory. Another object of this invention is to provide a conducting metal coating to the refractory Without the use of a flux. A further object of this invention is to provide a new article of manufacture consisting of a refractory to which a conducting metal is caused to adhere firmly. A more specific object is to provide a new article of manufacture consisting of a zircon refractory to which has been caused to adhere a firm coating of a conducting metal. Another more specific object is to provide methods for the manu facture of the aforementioned zircon coated with a conducting metal. These and other objects will be apparent from the description which follows.

The novelty of the present invention lies in applicants discovery that the refractory zircon will be thoroughly wetted by such conducting metals as copper, silver, and alloys of copper-silver when said metals are in a molten condition. The wetting may also be effected under pressure under which condition temperatures, which are about 100 F. below the melting point of the metal or alloy used, may be employed.

The present invention will be more completely understood by reference to the following examples.

Example I A rod of Zircon (lx%.x /z") was immersed in molten silver for five minutes and thereafter allowed to cool gradually to room temperature. The resulting article was examined under a microscope and showed that the zircon had been wetted or impregnated by the silver. Moreover, the article was also characterized by having (a) a hardness greater than the original zircon and comparable to silicon carbide, (b) the conductivity of a metal, and (c) the porosity of the original zircon rod. In addition an X-ray diffraction analysis and an acid dis solution test disclosed that the absorption of the copper is primarily physical and not due to the formation of a new phase.

Example II The procedure of Example I was repeated with similar results except the metal was a copper-silver alloy (#301 Silvaloy) consisting of 72% silver and 28% copper, and the heating was carried out at a temperature of 1750 F for ten minutes in a slightly oxidized furnace.

Example III The procedure of Example I is repeated with similar results except the metal is copper and the heating is carried out under strong oxidizing conditions for 7 minutes.

In each of the above examples the metallic coated zircon article did not develop any crack between the metal and zircon upon cooling to room temperature although the thermal expansion of the zircon is only about one-half that of the metal coating whether it be copper, silver or a silver-copper alloy. In fact when the article of Example II was heated in a furnace up to 2000 F. for thirty minutes and then quenched in cold water, no crack developed between the zircon and alloy.

Example IV Zircon sand of 40 mesh size was mixed with an equal amount of copper and heated to fuse the copper and bond the zircon together. Upon cooling the resulting product was examined under a microscope and was found to consist of an integral, hard, dense mass of copper and zircon indicating a complete wetting of the zircon by the copper since no crack or void was observed between the zircon and copper interfaces.

Example V The procedure of Example IV was repeated with the same excellent results except the zircon sand was of 200 mesh size and the metal was silver.

Example VI The procedure of Example IV was repeated except the zircon and copper were heated to 1900 F. under a pressure of 50 lbs/sq. in.

Example VII The procedure of Example V was repeated except the zircon and silver were heated at 1700 F. under a pressure of 50 lbs/sq. in.

Example VIII The procedure of Example IV was repeated except Silvaloy was substituted for the copper; and the zircon and Silvaloy were heated at 1400 F. under a pressure of 50 lbs/sq. in.

The foregoing examples are presented merely as typical illustrations of the present invention; and it is not intended that the inventive concept herein disclosed is to be limited thereby. Moreover, numerous modifications can be made which will be apparent to those skilled in the art and which are contemplated by the invention herein set forth.

In general the temperature at which the zircon is coated by the metal or alloy will vary from l500 to 1980 F. by the immersion or soaking process which is usually completed in about 5 to 10 minutes, depending upon the porosity of the zircon. In general the more porous the zircon, the shorter the soaking period. Actually the metal or alloy can be applied at temperatures ranging from 1450 to 1950 F. The zircon whether in rod form (Examples IIII above) or in particle form (Examples IV-VI above) will be more completely wetted by the metal or alloy where the zircon is more porous and the immersion or soaking takes place at higher temperature and for longer periods of time.

In addition it is to be understood that the metal or alloy may be applied by other than an immersion or soaking method. Thus the metal or alloy can be applied in the molten state at the above temperatures to the zircon as a flame spray by using a gun of the Schoop type.

For certain application as noted above (Examples IV, V, VI, VII, and VIII) it was found practicable to make a powder mixture of the metal and zircon; and heat or heat and press the mixture into the desired shape in a mold. The following temperatures have proven satisfactory with the mixtures set forth below.

Mixture: Temperature, F. Zircon-copper 1900-10-50 Zircon-silver 1700-1750 Zircon#301 Silvaloy 1400-14-50 The products formed can be described as having been formed by a complete wetting of the zircon particles by the molten metal followed by a solidification in which the zircon particles are united into a firm adherent mass by the coating of the molten metal particles to the solid state. The foregoing molded products are useful where either a more complete permeation of larger zircon articles by the molten metal is desired or the metallic properties of the resulting composite article need to be accentuated. Where considerable pressures are applied to form the articles, lower temperatures may be employed than noted above. Since the bonding of the zircon to the metal or alloy is a wetting phenomenon or substantially mechanical in nature rather than chemical, the ratio of zircon to metal or alloy can vary greatly such that the zircon to copper can be in the ratio of 1:10 as well as 10:1 and any intermediate range.

Although zircon is usually considered as having the composition of ZrO -SiO it is to be understood that the present invention is applicable to the commercial varieties of zircon which contain from 90 to 95% ZrO -SiO and 5 to of other constituents or impurities such as CaO-MgO.

Various other copper-silver alloys can be employed in the present invention including coin silver (90% silver 10% copper) and standard silver (92.5% silver and 7.5% copper).

The articles produced according to this invention are of great practical utility. Since zircon has good chemical resistance, high melting point, a high degree of hardness, a high thermal shock resistance, and low thermal expansion whereas silver, copper and silver-copper alloys have high thermal and electrical conductivities, the articles of Examples I, II, and III above, by way of illustration, can be used as (1) electric contacts and as (2) abrasive and chemical resistant facings besides other uses which will be apparent to those skilled in the art where it is desired to employ the combined properties of materials such as zircon and metals like copper and silver.

While the illustrative embodiments of the invention have been described hereinbefore with particularity, it will be understood that various other modifications will be apparent to and can readily be made by those skilled in the art without departing from the scope and spirit of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and description set forth herein but rather the claims be construed as encompassing all the features of patentable novelty which reside in the present invention including all features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains.

What is claimed is:

1. A new article of manufacture consisting of particles of zircon which are thoroughly wetted and bound together by a solidized liquid phase consisting of a metal selected from the group consisting of copper, silver and coppersilver alloys.

2. In a method of making a conductive zircon article, the steps consisting of (a) immersing the zircon in a molten metal selected from the group consisting of silver, copper, and silver-copper alloys and (b) cooling the resulting article to room temperature.

3. The method of claim 2 in which the immersion period is from 5 to 10 minutes.

4. In a method of making a formed conductive zircon article, the steps comprising (a) contacting particles of zircon with a metal at a temperature from about 1400 to about 1950 F. and which is selected from the group consisting of silver, copper, and silver-copper alloys; (12) press forming the same in a mold to the desired shape; and (c) cooling the resulting article to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS 893,933 Monnot July 21, 1908 1,851,699 Frey Mar. 29, 1932 2,042,635 Schellens June 2, 1936 2,200,087 Kelly May 7, 1940 2,244,052 Comstock June 3, 1941 2,370,242 Hensel et al Feb. 27, 1945 2,642,654 Ahrens Jan. 23, 1953 2,724,892 Knochel Nov. 29, 1955 2,950,995 Place et al Aug. 30, 1960 

1. A NEW ARTICLE OF MANUFACTURE CONSISTING OF PARTICLES OF ZIRCON WHICH ARE THOROUGHLY WETTED AND BOUND TOGETHER BY A SOLIDIZED LIQUID PHASE CONSISTING OF A METAL SELECTED FROM THE GROUP CONSISTING OF COPPER, SILVER AND COPPERSILVER ALLOYS. 